1. Field of the Invention
The present invention relates to an image output device, an image output method, and a computer program product.
2. Description of the Related Art
In an image output device, even if the same image data is output, the density of output images may vary due to time degradation of a developing material; therefore, for the purpose of suppressing a temporal variation in density, the image output device outputs a predetermined patch and causes a scanner or the like to read the patch, thereby perceiving tone characteristics at the time, and generates a tone correction parameter.
In such an image output device, however, the density may still vary according to locations within output images that are based on the same image data. This occurs due to the quality of a member or the assembly accuracy, for example, in an electrophotographic image output device, due to the eccentricities of a photosensitive element and a transfer roller or a variation in distance between the photosensitive element and a developing sleeve along a rotating direction of the photosensitive element.
Namely, a photosensitive drum and a developing sleeve have eccentricities which cannot be suppressed in view of the design accuracy, and an interval between them varies according to respective rotation angles, so an amount of color material varies, and the density varies; that is why a density variation in a rotating direction of the photosensitive drum occurs. In general, a rotation angle of a rotating body including the photosensitive drum is not synchronized with the position of a sheet, so the locations showing the high density and the low density and further the location showing the medium density vary from page to page. Therefore, when the density of a patch is measured only at a specific point on a page, in addition to a temporal density variation, a density variation due to a difference in location caused by the eccentricity of the rotating body, such as the photosensitive drum, is also contained. Consequently, an appropriate tone correction parameter for suppressing the temporal density variation is not obtained.
Conventionally, a parameter is generated using one patch. To cope with the above-mentioned problem, there has been proposed a device that generates a plurality of patches having the same density tone level on a sheet at appropriate intervals in a rotating direction of a photosensitive drum. The device generates a tone correction parameter by averaging values obtained by measuring the densities of the patches, thereby perceiving tone characteristics at the time when the patches are output while suppressing the effect of a phenomenon that the density varies according to locations within images. The device generates a density correction processing parameter for suppressing a temporal density variation (for example, see Japanese Patent Application Laid-open No. 2000-103147, Japanese Patent Application Laid-open No. 2008-209436, and Japanese Patent Application Laid-open No. 2009-38734).
In such conventional technologies, the temporal density variation can be suppressed and images at the constant density can be output; however, they have not assumed the function to change the accuracy of outputting an image at the constant density. Namely, a user cannot arbitrarily set the image output accuracy, and an image with an image output accuracy which the user desires cannot be output.